Process of producing sheet metal structures



March 18, 1969 A. PERLICK ETAL PROCESS OF PRODUCING SHEET METAL STRUCTURES Filed Oct. 21. 19654 z 2 *2/ 2 3/ f XYXX 2K XXXXXX s 2 g" 2 6 6 2 0 o o l I/ LI; XxxxXxxxxx X X \X\ T I 5 5 5 3 Fig.2

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UHHHHIIIHIIIIIIIIHIIHIIH m 1 IIHHHHIIIHIHIHIIIIIIHIH 70 Fig-4 Inventors 1 AL EEAW- Pen m/v A); FRED G me as United States Patent 3,432,903 PROCESS OF PRUDUCING SHEET METAL STRUCTURES Albert Perlick, Werdohl-Kleinhammer, and Alfred Gareis,

Werdohl-Eveking, Germany, assignors to Vereinigte Deutsche Metallwerke AG, Frankfurt am Main, Heddernheim, Germany, a corporation of Germany Filed Oct. 21, 1965, Ser. No. 500,375 Claims priority, application Germany, Dec. 29, 1964,

47 US. or. 29-1575 Int. Cl. B21d 53/00; szik 29/00 11 Claims ABSTRACT OF THE DISCLOSURE The invention relates to sheet metal structures and a process of producing such a structure.

The invention provides a process for the annealing of hard sheet metal in which thin non-metallic layers are included at various places. Such sheets constitute an intermediate product in the manufacture of sheet metal parts containing cavities, which are used as so-called coil plates or channel plates for heat exchangers or as flat components in which great rigidity combined with low weight is desirable. In the manufacturing process, a piece of sheet metal is first printed at various places with a non-metallic parting agent that impedes welding, such as graphite, for example. The printed side of this first plate is then covered with a second plate of equal size. The two plates are then bonded together by pressure welding (rolling, for example) at the areas free of parting agent. The intermediate product thus obtained, namely a sheet metal sandwich in which thin, non-metallic layers are included at various points, has been subjected to severe mechanical Working, that is, it has been workhardened, and so it must be annealed soft before cavities can be blown (with compressed air, for example) in the areas where the thin layers of parting agents are located, that is, where the plate is to be expanded. Annealing increases ductility, but reduces mechanical strength. The manufacturing process which has been described can be performed with all metals that can be pressure-Welded, such as aluminum, copper, silver and their alloys with other metals, as well as stainless steel. Aluminum is especially suitable, because it can be welded by hot rolling in the open air, i.e., without shielding gas. Coil plates made of aluminum are especially well known in the form of refrigerator evaporators.

It is customary to anneal the intermediate product, namely, the hard, unblown plates, slowly in stacks over a period of several hours, or to anneal them quickly individually over a bed of flames. In both cases, the entire plate becomes soft, that is, including the areas in which no non-metallic layers are contained, and whose ductility therefore does not have to be increased; this is disadvantageous. An annealed intermediate product that would be soft and ductile only where the cavities are to be blown would offer considerable advantages: it would be mechanically stronger and could therefore be thinner and lighter than one that is soft all over. If only the areas 3,432,003 Patented Mar. 18, 1969 corresponding to the non-metallic layers could be annealed on only one side, then, when the channels are blown, they would expand only on one side, while the other side, which would remain hard all over, would stay fiat or substantially flat.

Now, the surprising observation has been made that the conduction of heat through the thin, non-metallic included layers is so poor that it is possible to anneal only one of the two walls enclosing the layer and to leave the other one hard. The following is given as an illustrative example: If a sandwich of pure aluminum plates, the sandwich being 1.5 mm. thick, between whose inner surfaces strips of graphite powder 10 mm. wide and 0.005 mm. thick are centrally located, is heated on one side with an oxygen-manufactured gas flame and is cooled with water from the opposite side, the one wall, 0.75 mm. thick, can even be fused while the opposite wall is nevertheless kept hard. The heated wall, therefore, can be annealed soft. Since the amount of heat that is required to heat the one wall is small in comparison to the total amount of heat that is put in and conducted away again through the opposite wall by the cooling water, a static temperature gradient must be established, which can be achieved only asymptotically.

It is the above observation that forms the basis for the process of the invention for the annealing of hard sheet metal in which thin, non-metallic layers are included in certain areas, and according to which a temperature gradient is forced between the exterior surfaces of the plate, whose upper limit is at least equal to the annealing temperature of the plate, and whose lower limit lies below this temperature. The temperature gradient can be provided by heating one exterior surface and cooling the other. The process can also be similar, however, to the one that is used in the art of surface-hardening steel pieces, namely, only one exterior surface is heated and the immediately adjacent area is cooled.

The plate can be heated in various prior art ways. In addition to flame heating, electrical induction heating can be used, the best frequency depending on the type of metal and the thickness of the plate. The plate can also be heated by the Joulean effect, in which case it is expedient to lay two plates of equal size one on the other and send an electrical current par-allelly through both together, while the outside surface of the double plate is being cooled.

It is in the prior art to produce aluminum sheet metal in which thin, non-metallic layers are included in certain areas by pressure welding together two sheets of different alloys by a rolling process. In a plate produced in this manner, the channel walls on the one side of the plate can then be obtained in a harder state than on the other if the entire plate is not uniformly annealed. However, only a few aluminum alloys can be roll-welded in the open air; for instance, a manganese content impairs welding but slightly, while a magnesium content greatly interferes with welding. The naturally harder metal elongates less when rolled than the softer one, and the result is that the two sheets slip one on the other in the roller gap; for one thing, this has an adverse effect on the printed-on parting agent layers. Furthermore, the scrap produced in the cutting of the finished channel plates consists of a mixture of alloys which cannot be reused directly by remelting.

The process of the invention can also be used, of course, in the case of channel plates made by the roll-welding of two sheets of different alloys. In this case, considerably greater differences in hardness can be obtained between the channel walls than in the case of a channel plate composed of metal sheets of identical composition.

Thus, the invention provides an improvement in the known process for production of open metal work wherein a sandwich of metal plates bonded together at loci which are to be bonded together in the open metal work and separated by a parting compound in areas to be expanded to provide the open metal work, is expanded by pressure applied between the plates. In the known process, prior to the expansion metal of each plate opposite the faces of the parting compound is in hardened condition, and the sandwich, also prior to the expansion, is conditioned for the expansion, by softening by annealing hardened metal opposite the parting agent. According to the invention, the softening by annealing is imparted to the metal opposite one of the faces of the parting agent, leaving the metal opposite the other of the faces of the parting agent in hardened condition. In consequence of this treatment, in the expansion, one of the sheets is expanded substantially more than the other.

By hardened or work hardened condition is meant a stressed condition resulting from substantial Working of the metal, and by softened or annealed condition is meant a condition wherein such stress condition is substantially absent.

The invention will be explained by way of example with the aid of the schematic drawings, in which identical numbers always identify corresponding parts.

FIG. 1 shows a plate which is heated from beneath by a flame and is cooled by water from above at an area opposite the flame; the plate is moved in the direction of the arrow, as it is in FIGS. 2 and 3.

In FIG. 2, the cooling area is divided into two cooling zones; otherwise the procedure is the same as in FIG. 1.

In FIG. 3, the temperature gradient is obtained workin g from only one exterior surface of a plate.

FIG. 4 depicts the cavity walls formed from a sandwich having soft channel walls on one side and hard walls on the other side.

The roller-hardened pure aluminum sandwich 1, which is 1.5 mm. thick and in which non-metallic layers 2 of graphite 0.005 mm. thick and 16 mm. wide are included in certain areas, is heated by the oxygen-manufactured gas flame 3 and cooled by water 4. In the arrangement of FIG. 1, a temperature gradient of around 500 C. is produced between the exterior surfaces of the plate, which is virtually linear where no layers 2 are located. Where, however, the thermal conduction in the plate is impaired by a layer 2, the temperature within layer 2 undergoes an abrupt transition from nearly 500 C. to approximately the temperature of the water. Therefore, the wall 5 on the flame side is annealed, which is indicated by the crosshatching. The wall 6 on the water side, however, remains hard.

Since the extremely great temperature gradient must be static, so that the plate will not melt through, in the arrangement of FIG. 1, a great deal of hot water is produced on account of the good thermal conductivity of aluminum, that is, a great deal of energy is dissipated. Hard, pure aluminum sheet can, however, be heated for several minutes at 350 C. without softening (for other metals, of course, other times and temperatures apply), and so it is not necessary to keep the one exterior side of plate 1 at water temperature. If the flow of water 4 should be decreased, the cooling would rapidly fail entirely, because the Leidenfrost phenomenon would occur. The water cooling could be replaced by liquid lead cooling; e.g., plate 1 could float on lead and be heated from above by a flame. The same purpose can be achieved more simply, however, if, as in FIG. 2, the cooling zone is divided into two zones. The distance between these zones may then not be substantially greater than layers 2 are wide, as it can easily be understood. The process can then be operated so that wall 6 becomes no hotter than 350 C., but well 5 heats up to 500 C. and, therefore, softens. The same is true for the embodiment of FIG. 3, wherein heating and cooling is effected from the same side. In this embodiment, the softening by annealing is effected b heating the metal to be softened and cooling the metal to be left in hardened condition, said cooling being effected by withdrawal of heat adjacent the metal to be softened and from 4 the side of the sandwich on which the metal to be softened is located. The flame baflies 7 define the cooling and flame zones. In this case, wall 8 is annealed soft, while wall 9 remains hard.

Lastly, FIG. 4 indicates how the soft walls 5 bulge in comparison to the hard walls 6 when, in the prior art manner, cavities are blown between flat holding plates 10 at points where thin non-metallic layers 2 are located, if the plate has been annealed according to the invention. Evidently, the hard walls 6 can also be kept flat if the soft walls 5 are blown into an elastic or plastic bed made, for example, of foam rubber or water, as it is done in the prior art with uniformly soft plates.

The particular conditions, such as cooling water rate and velocity of the sandwich, can be selected according to the particular annealing operation to be effected. This can be determined by trial and error, and, if desired, temperature indicating means such as thermo-couples can be utilized in trial runs to determine suitable operating conditions.

While the invention has been described with respect to particular embodiment thereof, these are merely representative and do not serve to define the limits of the invention.

What is claimed is:

.1. In a process for production of open metal work wherein a sandwich of metal plates bonded together at loci which are to be bonded together in the open metal work and separated by a parting agent in areas to be expanded to provide the open metal work, is expanded by pressure applied between the plates, and wherein prior to the expansion, metal of each plate opposite the faces of the parting compound is in hardened condition, the improvement which comprises softening by annealing the metal opposite one of the faces of the parting agent leaving the metal opposite the other of the faces of the parting agent in hardened condition, so that in the expansion, one of the sheets is expanded substantially more than the other, the annealing being effected by providing a temperature gradient across the thickness of the sandwich, the gradient being such that the temperature of metal to be softened is at least equal to the annealing temperature of that metal, while the temperature of the metal to remain hard is below the annealing temperature thereof.

2. Process according to claim 1, wherein the metal plates are of substantially the same composition.

3. Process according to claim 1, wherein the metal annealed is heated and the metal left in hardened condition is cooled by passing a cooling medium in contact therewith.

4. Process according to claim 3, wherein said cooling medium is water.

5. Process according to claim 2, wherein the metal annealed is heated and the metal left in hardened condition is cooled by passing a cooling medium in contact therewith.

*6. Process according to claim 5, wherein said cooling medium is water.

7. Process according to claim 1, wherein the softening by annealing is effected by heating the metal to the softened and cooling the metal to be left in hardened condition, said cooling being effected by withdrawal of heat adjacent the metal to be softened and from the side of the sandwich on which the metal to be softened is located.

8. Process according to claim 7, wherein said cooling is effected by contacting water with the sandwich.

9. Process according to claim 2, wherein the softening by annealing is effected by heating the metal to the softened and cooling the metal to be left in hardened condition, said cooling being effected by withdrawal of heat adjacent the metal to be softened and from the side of the sandwich on which the metal to be softened is located.

5 6 10. Process according to claim 9, wherein said cooling 3,046,649 7/ 1962 Brennan 29-498 X is effected by contacting water with the sandwich. 3,053,514 9/1962 Grenell 29-157.3 11. Process according to claim 1, wherein said plates 3,108,361 10/1963 Neel 29-157.3 are aluminum of the same composition. 3,222,763 12/1965 Heuer 29-498 X References Cited 5 JOHN F. CAMPBELL, Primary Examiner. UNITED STATES PATENTS D. C. REILEY, Assistant Examiner. 2,294,413 9/1942 Marshall 148-148 3,196,528 7/1965 Broverman et a1. 29-157.3

3,015,157 1/1962 Reynolds et a1. 29-498 X 10 148-148 

